Multiple arm trials
This section contains the following:
Introduction
A simple extension of the two-arm trial is to randomize
participants
to more than two groups. For example, in a three-arm trial the
intervention groups receive
two
different doses of a drug while the control group receives a
placebo. Such trials can be designed and conducted with
relatively
fewer
additional resources, compared to a two-arm trial, and allow
investigation
of the relative effectiveness of two (or more) interventions.
These
benefits can be compromised by a loss of statistical power. For
example,
the sample size for a three-arm trial needs to be increased by 50% to
achieve
the same power as a two-arm trial. The Trial Protocol Tool can
also be used to support the development of protocols for multiple arm
trials. See Further reading
for
more details.
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Illustrative example - From the Annals of
Surgery
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A randomized multicenter three-armed trial comparing
laparoscopic mesh with open preperitoneal mesh with conventional
technique for inguinal hernia repair (SCUR Hernia Repair Study). (Annals
of Surgery 1999; 230(2):225-231 )
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Illustrative example - From the American
Journal of Surgery
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A prospective randomized study comparing laparoscopic and open
tension-free inguinal hernia repair with Shouldice. (The American
Journal of Surgery 1998; 175:331-333)
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Further reading
Pocock SJ. Clinical Trials: A Practical Approach. Chichester: John
Wiley and Sons, 1983.
Duley L and Farrell B. Clinical Trials. London: BMJ Books, 2002.
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This page was last updated 20th May 2005.